Process for producing polyolefins

ABSTRACT

A novel process for producing homopolymers and interpolymers of olefins which involves contacting an olefin and/or an olefin and at least one or more other olefin(s) under polymerization conditions with an olefin polymerization catalyst and dinitrogen monoxide in an amount sufficient to reduce the electrostatic charge in the polymerization medium. Also provided is a process for reducing electrostatic charge in the polymerization of an olefin by adding dinitrogen monoxide.

FIELD OF INVENTION

The present invention relates to a polymerization process for theproduction of polyolefins utilizing a catalyst suitable for polymerizingolefins and dinitrogen monoxide in amounts sufficient to reduce theelectrostatic charge in the polymerization reactor. The use ofdinitrogen monoxide as a catalytic agent further provides polyolefinsthat are suitable for molding and film applications.

BACKGROUND OF INVENTION

Polyolefins such as polyethylene are well known and are useful in manyapplications. In particular, linear polyethylene polymers possessproperties which distinguish them from other polyethylene polymers, suchas branched ethylene homopolymers commonly referred to as LDPE (lowdensity polyethylene). Certain of these properties are described byAnderson et al, U.S. Pat. No. 4,076,698.

A particularly useful polymerization medium for producing polyethyleneand polypropylene polymers is a gas phase process. Examples of such aregiven in U.S. Pat. Nos. 3,709,853; 4,003,712; 4,011,382; 4,302,566;4,543,399; 4,882,400; 5,352,749 and 5,541,270 and Canadian Patent No.991,798 and Belgian Patent No. 839,380.

There are known various catalysts for polymerizing olefins. Exemplary ofsuch catalysts are as follow:

1. Chromium oxide catalysts which polymerize ethylene to high molecularweight high density polyethylenes (HDPE) having a broad molecular weightdistribution. These catalysts are typically based on Cr(6+) and aresupported on a carrier.

2. Organochromium catalysts such as bis(triphenylsilyl)chromatesupported on silica and activated with organoaluminum compounds, andbis(cyclopentadienyl)chromium supported on silica.

3. Ziegler-Natta catalysts which typically consist of a transition metalcomponent and an organometallic co-catalyst that is typically anorganoaluminum compound.

4. An olefin polymerization catalyst that polymerizes olefins to producehomopolymers and interpolymers of olefins having a molecular weightdistribution (MWD) of from 1 to 2.5.

5. Metallocene catalysts which typically consist of a transition metalhaving at least one substituted or unsubstituted cyclopentadienyl orcyclopentadienyl moiety, and an organometallic co-catalyst that istypically alkyl aluminoxane, such as methyl aluminoxane, or an arylsubstituted boron compound.

6. Group 13 catalysts of this type described in U.S. Pat. No. 5,777,120,such as cationic aluminum alkyl amidinate complexes with anorganometallic co-catalyst that is typically alkylaluminoxane, such asmethylaluminoxane, or an aryl substituted boron compound.

7. Catalysts of the type described in U.S. Pat. No. 5,866,663, such ascationic nickel alkyl diimine complexes with an organometallicco-catalyst that is typically alkylaluminoxane, such asmethylaluminoxane, or an aryl substituted boron compound.

8. Catalysts of the type described in Organometallics, 1998, Volume 17,pages 3149-3151, such as neutral nickel alkyl salicylaldiminatocomplexes.

9. Catalysts of the type described in the Journal of the AmericanChemical Society, 1998, Volume 120, pages 7143-7144, such as cationiciron alkyl pyridinebisimine complexes with an organometallic co-catalystthat is typically alkylaluminoxane, such as methylaluminoxane, or anaryl substituted boron compound.

10. Catalysts of the type described in the Journal of the AmericanChemical Society, 1996, Volume 118, pages 10008-10009, such as cationictitanium alkyl diamide complexes with an organometallic co-catalyst thatis typically alkylaluminoxane, such as methylaluminoxane, or an arylsubstituted boron compound.

The above catalysts are, or can be, supported on inert porousparticulate carrier.

A generally encountered problem in polymerization processes, inparticular gas phase polymerization processes, is the formation ofagglomerates. Agglomerates can form in various places such as thepolymerization reactor and the lines for recycling the gaseous stream.As a consequence of agglomerate formation it may be necessary to shutdown the reactor.

When agglomerates form within the polymerization reactor there can bemany adverse effects. For example, the agglomerates can disrupt theremoval of polymer from the polymerization reactor by plugging thepolymer discharge system. Further, if the agglomerates fall and coverpart of the fluidization grid a loss of fluidization efficiency mayoccur. This can result in the formation of larger agglomerates which canlead to the loss of the entire fluidized bed. In either case there maybe the necessity for the shutdown of the reactor.

It has been found that agglomerates may be formed as a result of thepresence of very fine polymer particles in the polymerization medium.These fine polymer particles may be present as a result of introducingfine catalyst particles or breakage of the catalyst within thepolymerization medium.

These fine particles are believed to deposit onto and electrostaticallyadhere to the inner walls of the polymerization reactor and theassociated equipment for recycling the gaseous stream such as, forexample, the heat exchanger. If the fine particles remain active, andthe polymerization reaction continues, then the particles will grow insize resulting in the formation of agglomerates. These agglomerates whenformed within the polymerization reactor tend to be in the form ofsheets.

Several solutions have been proposed to resolve the problem of formationof agglomerates in gas phase polymerization processes. These solutionsinclude the deactivation of the fine polymer particles, control of thecatalyst activity and the reduction of the electrostatic charge.Exemplary of the solutions are as follows.

European Patent Application 0 359 444 A1 describes the introduction intothe polymerization reactor of small amounts of an activity retarder inorder to keep substantially constant either the polymerization rate orthe content of transition metal in the polymer produced. The process issaid to produce a polymer without forming agglomerates.

U.S. Pat. No. 4,739,015 describes the use of gaseous oxygen containingcompounds or liquid or solid active-hydrogen containing compounds toprevent the adhesion of the polymer to itself or to the inner wall ofthe polymerization apparatus.

In U.S. Pat. No. 4,803,251 there is described a process for reducingsheeting utilizing a group of chemical additives which generate bothpositive and negative charges in the reactor, and which are fed to thereactor in an amount of a few parts per million (ppm) per part of themonomer in order to prevent the formation of undesired positive ornegative charges.

Other processes and other additives that may be used to neutralizeelectrostatic charge in the fluidized-bed reactor are found in U.S. Pat.Nos. 4,792,592; 4,803,251; 4,855,370; 4,876,320; 5,162,463; 5,194,526and 5,200,477.

Additional processes for reducing or eliminating electrostatic chargeinclude (1) installation of grounding devices in a fluidized bed, (2)ionization of gas or particles by electrical discharge to generate ionswhich neutralize electrostatic charge on the particles and (3) the useof radioactive sources to produce radiation capable of generating ionswhich neutralize electrostatic charge on the particles.

It would be desirable therefore to provide a process for producingpolyolefins, particularly polyethylene, wherein the problems associatedwith electrostatic charge are reduced.

SUMMARY OF THE INVENTION

The polymerization process of the present invention comprises theintroduction into a polymerization medium comprising an olefin,particularly ethylene, and optionally at least one or more otherolefin(s), an olefin polymerization catalyst and dinitrogen monoxide(N₂O) in an amount sufficient to reduce the electrostatic charge in thepolymerization medium to a level lower than would occur in the samepolymerization process in the absence of dinitrogen monoxide.

The present invention also relates to a process for reducingelectrostatic charge in the polymerization of an olefin, particularlyethylene, and optionally at least one or more other olefin(s) in apolymerization medium, particularly gas phase, in the presence of anolefin polymerization catalyst, and dinitrogen monoxide (N₂O) in anamount sufficient to reduce electrostatic charge in the polymerizationmedium to a level lower than would occur in the same polymerizationprocess in the absence of the dinitrogen monoxide.

All mention herein to elements of Groups of the Periodic Table are madein reference to the Periodic Table of the Elements, as published in“Chemical and Engineering News”, 63(5), 27, 1985. In this format, theGroups are numbered 1 to 18.

DETAILED DESCRIPTION OF THE INVENTION

The polymerization process of the present invention comprises theintroduction into a polymerization medium comprising an olefin,particularly ethylene, and optionally at least one or more otherolefin(s), an olefin polymerization catalyst and dinitrogen monoxide(N₂O) in an amount sufficient to reduce the electrostatic charge in thepolymerization medium to a level lower than would occur in the samepolymerization process in the absence of the dinitrogen monoxide.

The present invention also relates to a process for reducingelectrostatic charge in the polymerization of an olefin, particularlyethylene, and optionally at least one or more other olefin(s) in apolymerization medium, particularly gas phase, in the presence of anolefin polymerization catalyst, and dinitrogen monoxide (N₂O) in anamount sufficient to reduce electrostatic charge in the polymerizationmedium to a level lower than would occur in the same polymerizationprocess in the absence of the dinitrogen monoxide.

Optionally a halogenated hydrocarbon may be added to the polymerizationmedium. Any halogenated hydrocarbon may be used in the process of thepresent invention. If desired more than one halogenated hydrocarbon canbe used. Typical of such halogenated hydrocarbons are monohalogen andpolyhalogen substituted saturated or unsaturated aliphatic, alicyclic,or aromatic hydrocarbons having 1 to 12 carbon atoms. Preferred for usein the process of the present invention are dichloromethane, chloroform,carbon tetrachloride, chlorofluoromethane, chlorodifluromethane,dichlorodifluoromethane, fluorodichloromethane, chlorotrifluoromethane,fluorotrichloromethane and 1,2-dichloroethane. Most preferred for use inthe process of the present invention is chloroform.

In the present invention, any catalyst for polymerizing olefins may beused. Preferably the olefin polymerization catalyst comprises at leastone metal selected from Groups 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and/or 13of the Periodic Table of the Elements, as defined herein. The olefinpolymerization catalyst may be neutral or cationic. Exemplary metals ofthe olefin polymerization catalyst are titanium, zirconium, vanadium,iron, chromium, nickel and aluminum. Exemplary of such polymerizationcatalysts are:

1. Any compound containing a Group 6 element. Preferred are chromiumcontaining compounds. Exemplary are chromium oxide catalysts whichpolymerize ethylene to high molecular weight high density polyethylenes(HDPE) having a broad molecular weight distribution. These catalysts aretypically based on Cr(6+) and are supported on a carrier. Furtherexemplary are organochromium catalysts such asbis(triphenylsilyl)chromate supported on silica and activated withorganoaluminum compounds, and bis(cyclopentadienyl)chromium supported onsilica.

2. Ziegler-Natta catalysts which typically consist of a transition metalcomponent and an organometallic co-catalyst that is typically anorganoaluminum compound.

3. An olefin polymerization catalyst that polymerizes olefins to produceinterpolymers of olefins having a molecular weight distribution (MWD) offrom 1 to 2.5.

4. Metallocene catalysts which consist of a transition metal componenthaving at least one moiety selected from substituted or unsubstitutedcyclopentadienyl, substituted or unsubstituted pentadienyl, substitutedor unsubstituted pyrrole, substituted or unsubstituted phosphole,substituted or unsubstituted arsole, substituted or unsubstitutedboratabenzene, and substituted or unsubstituted carborane, and anorganometallic co-catalyst that is typically alkyl aluminoxane, such asmethyl aluminoxane, or an aryl substituted boron compound.

5. Any compound containing a Group 13 element. Preferred are aluminumcontaining compounds. Exemplary are catalysts of the type described inU.S. Pat. No. 5,777,120, such as cationic aluminum alkyl amidinatecomplexes with an organometallic co-catalyst that is typicallyalkylaluminoxane, such as methylaluminoxane, or an aryl substitutedboron containing compound.

6. Any compound containing a Group 10 element. Preferred are nickelcontaining compounds. Exemplary are catalysts of the type described inU.S. Pat, No. 5,866,663, such as cationic nickel alkyl diimine complexeswith an organometallic co-catalyst that is typically alkylaluminoxane,such as methylaluminoxane, or an aryl substituted boron containingcompound. Further exemplary are catalysts of the type described inOrganometallics, 1998, Volume 17, pages 3149-3151, such as neutralnickel alkyl salicylaldiminato complexes.

7. Any compound containing a Group 8 element. Preferred are ironcontaining compounds. Exemplary are catalysts of the type described inthe Journal of the American Chemical Society, 1998, Volume 120, pages7143-7144, such as cationic iron alkyl pyridinebisimine complexes withan organometallic co-catalyst that is typically alkylaluminoxane, suchas methylaluminoxane, or an aryl substituted boron containing compound.

8. Any compound containing a Group 4 element. Preferred are titanium andzirconium containing compounds. Exemplary are catalysts of the typedescribed in the Journal of the American Chemical Society, 1996, Volume118, pages 10008-10009, such as cationic titanium alkyl diamidecomplexes with an organometallic co-catalyst that is typicallyalkylaluminoxane, such as methylaluminoxane, or an aryl substitutedboron containing compound.

The above catalysts are, or can be, supported on inert porousparticulate carriers.

The above olefin polymerization catalysts can be introduced in theprocess of the present invention in any manner. For example, thecatalyst component(s) can be introduced directly into the polymerizationmedium in the form of a solution, a slurry or a dry free flowing powder.The catalyst if requiring a co-catalyst can be premixed to form anactivated catalyst prior to addition to the polymerization medium, orthe components can be added separately to the polymerization medium, orthe components can be premixed and then contacted with one or moreolefins to form a prepolymer and then added to the polymerization mediumin prepolymer form. When the catalyst components are premixed prior tointroduction into the reactor, any electron donor compound may be addedto the catalyst to control the level of activity of the catalyst.Furthermore during the polymerization reaction being carried out in thepresence of the olefin polymerization catalyst, as above described,there may be added additional organometallic compound(s). The additionalorganometallic compounds may be the same or different from that used asco-catalyst.

Any or all of the components of the olefin polymerization catalysts canbe supported on a carrier. The carrier can be any particulate organic orinorganic material. Preferably the carrier particle size should not belarger than about 200 microns in diameter. The most preferred particlesize of the carrier material can be easily established by experiment.Preferably, the carrier should have an average particle size of 5 to 200microns in diameter, more preferably 10 to 150 microns and mostpreferably 20 to 100 microns.

Examples of suitable inorganic carriers include metal oxides, metalhydroxides, metal halogenides or other metal salts, such as sulphates,carbonates, phosphates, nitrates and silicates. Exemplary of inorganiccarriers suitable for use herein are compounds of metals from Groups 1and 2 of the Periodic Table of the Elements, such as salts of sodium orpotassium and oxides or salts of magnesium or calcium, for instance thechlorides, sulphates, carbonates, phosphates or silicates of sodium,potassium, magnesium or calcium and the oxides or hydroxides of, forinstance, magnesium or calcium. Also suitable for use are inorganicoxides such as silica, titania, alumina, zirconia, chromia, boron oxide,silanized silica, silica hydrogels, silica xerogels, silica aerogels,and mixed oxides such as talcs, silica/chromia, silica/chromia/titania,silica/alumina, silica/titania, silica/magnesia,silica/magnesia/titania, aluminum phosphate gels, silica co-gels and thelike. The inorganic oxides may contain small amounts of carbonates,nitrates, sulfates and oxides such as Na₂CO₃, K₂CO₃, CaCO₃, MgCO₃,Na₂SO₄, Al₂(SO₄)₃, BaSO₄, KNO₃, Mg(NO₃)₂, Al(NO₃)₃, Na₂O, K₂O and Li₂O.Carriers containing at least one component selected from the groupconsisting of MgCl₂, SiO₂, Al₂O₃ or mixtures thereof as a main componentare preferred.

Examples of suitable organic carriers include polymers such as, forexample, polyethylene, polypropylene, interpolymers of ethylene andalpha-olefins, polystyrene, functionalized polystyrene, polyamides andpolyesters.

The Ziegler-Natta catalysts are well known in the industry. TheZiegler-Natta catalysts in the simplest form are comprised of acomponent comprising at least one transition metal and a co-catalystcomprising at least one organometallic compound. The metal of thetransition metal component is a metal of Groups 4, 5, 6, 7, 8, 9 and/or10 of the Periodic Table of the Elements, as published in “Chemical andEngineering News”, 63(5), 27, 1985. In this format, the groups arenumbered 1-18. Exemplary of such transition metals are titanium,zirconium, vanadium, chromium, manganese, iron, cobalt, nickel, and thelike, and mixtures thereof. In a preferred embodiment the transitionmetal is selected from the group consisting of titanium, zirconium,vanadium and chromium, and in a still further preferred embodiment, thetransition metal is titanium. The Ziegler-Natta catalyst can optionallycontain magnesium and/or chlorine. Such magnesium and chlorinecontaining catalysts may be prepared by any manner known in the art.

The co-catalyst used in the process of the present invention can be anyorganometallic compound, or mixtures thereof, that can activate thetransition metal component in a Ziegler-Natta catalyst in thepolymerization of olefins. In particular, the organometallic co-catalystcompound that is reacted with the transition metal component contains ametal of Groups 1, 2, 11, 12, 13 and/or 14 of the above describedPeriodic Table of the Elements. Exemplary of such metals are lithium,magnesium, copper, zinc, boron, silicon and the like, or mixturesthereof.

Preferably the co-catalyst is at least one compound of the formula,

X_(n)ER_(3-n),

or mixtures thereof,

wherein,

X is hydrogen, halogen, or mixtures of halogens, selected from fluorine,chlorine, bromine and iodine;

n ranges from 0 to 2;

E is an element from Group 13 of the Periodic Table of Elements such asboron, aluminum and gallium; and

R is a hydrocarbon group, containing from 1 to 100 carbon atoms and from0 to 10 oxygen atoms, connected to the Group 13 element by a carbon oroxygen bond.

Exemplary of the R group suitable for use herein is C₁₋₁₀₀ alkyl, C₁₋₁₀₀alkoxy, C₂₋₁₀₀ alkenyl, C₄₋₁₀₀ dienyl, C₃₋₁₀₀ cycloalkyl, C₃₋₁₀₀cycloalkoxy, C₃₋₁₀₀ cycloalkenyl, C₄₋₁₀₀ cyclodienyl, C₆₋₁₀₀ aryl,C₇₋₁₀₀ aralkyl, C₇₋₁₀₀ aralkoxy and C₇₋₁₀₀ alkaryl. Also exemplary ofthe R group are hydrocarbons containing from 1 to 100 carbon atoms andfrom 1 to 10 oxygen atoms.

Exemplary of the co-catalyst used in the process of the presentinvention where n=0 are trimethylaluminum; triethylborane;triethylgallane; triethylaluminum; tri-n-propylaluminum;tri-n-butylaluminum; tri-n-pentylaluminum; triisoprenylaluminum;tri-n-hexylaluminum; tri-n-heptylaluminum; tri-n-octylaluminum;triisopropylaluminum; triisobutylaluminum;tris(cylcohexylmethyl)aluminum; dimethylaluminum methoxide;dimethylaluminum ethoxide; diethylaluminum ethoxide and the like.Exemplary of compounds where n=1 are dimethylaluminum chloride;diethylaluminum chloride; di-n-propylaluminum chloride;di-n-butylaluminum chloride; di-n-pentylaluminum chloride;diisoprenylaluminum chloride; di-n-hexylaluminum chloride;di-n-heptylaluminum chloride; di-n-octylaluminum chloride;diisopropylaluminum chloride; diisobutylaluminum chloride;bis(cylcohexylmethyl)aluminum chloride; diethylaluminum fluoride;diethylaluminum bromide; diethylaluminum iodide; dimethylaluminumhydride; diethylaluminum hydride; di-n-propylaluminum hydride;di-n-butylaluminum hydride; di-n-pentylaluminum hydride;diisoprenylaluminum hydride; di-n-hexylaluminum hydride;di-n-heptylaluminum hydride; di-n-octylaluminum hydride;diisopropylaluminum hydride; diisobutylaluminum hydride;bis(cylcohexylmethyl)aluminum hydride; chloromethylaluminum methoxide;chloromethylaluminum ethoxide; chloroethylaluminum ethoxide and thelike. Exemplary of compounds where n=2 are methylaluminum dichloride;ethylaluminum dichloride; n-propylaluminum dichloride; n-butylaluminumdichloride; n-pentylaluminum dichloride; isoprenylaluminum dichloride;n-hexylaluminum dichloride; n-heptylaluminum dichloride; n-octylaluminumdichloride; isopropylaluminum dichloride; isobutylaluminum dichloride;(cylcohexylmethyl)aluminum dichloride and the like. Also exemplary arealkylaluminum sesquialkoxides such as methylaluminum sesquimethoxide;ethylaluminum sesquiethoxide; n-butylaluminum sesqui-n-butoxide and thelike. Also exemplary are alkylaluminum sesquihalides such asmethylaluminum sesquichloride; ethylaluminum sesquichloride;isobutylaluminum sesquichloride; ethylaluminum sesquifluoride;ethylaluminum sesquibromide; ethylaluminum sesquiiodide and the like.

Preferred for use herein as co-catalysts are trialkylaluminums such astrimethylaluminum, triethylaluminum, tri-n-propylaluminum,tri-n-butylaluminum, triisobutylaluminum, tri-n-hexylaluminum,triisohexylaluminum, tri-2-methylpentylaluminum, tri-n-octylaluminum,tri-n-decylaluminum; and dialkylaluminum halides such asdimethylaluminum chloride, diethylaluminum chloride, dibutylaluminumchloride, diisobutylaluminum chloride, diethylaluminum bromide anddiethylaluminum iodide; and alkylaluminum sesquihalides such asmethylaluminum sesquichloride, ethylaluminum sesquichloride,n-butylaluminum sesquichloride, isobutylaluminum sesquichloride,ethylaluminum sesquifluoride, ethylaluminum sesquibromide andethylaluminum sesquiiodide.

Most preferred for use herein as co-catalysts are trialkylaluminums suchas trimethylaluminum, triethylaluminum, tri-n-propylaluminum,tri-n-butylaluminum, triisobutylaluminum, tri-n-hexylaluminum,triisohexylaluminum, tri-2-methylpentylaluminum, tri-n-octylaluminum anddialkylaluminum halides such as dimethylaluminum chloride,diethylaluminum chloride, dibutylaluminum chloride, diisobutylaluminumchloride and alkylaluminum sesquihalides such as methylaluminumsesquichloride, ethylaluminum sesquichloride, n-butylaluminumsesquichloride and isobutylaluminum sesquichloride.

Mixtures of the above co-catalysts also can be utilized herein as theco-catalyst.

Furthermore there may be added to the Ziegler-Natta catalysts anyelectron donor. The electron donor compound preferably is selected fromthe group consisting of ethers, thioethers, esters, thioesters, amines,amides, ketones, nitriles, phosphines, silanes, acid anhydrides, acidhalides, acid amides, aldehydes, and organic acid derivatives. Morepreferred as electron donors are compounds containing from 1 to 50carbon atoms and from 1 to 30 heteroatoms of an element, or mixturesthereof, selected from Groups 14, 15, 16 and 17 of the Periodic Table ofElements.

The Ziegler-Natta catalyst may be prepared by any method known in theart. The catalyst can be in the form of a solution, a slurry or a dryfree flowing powder. The amount of Ziegler-Natta catalyst used is thatwhich is sufficient to allow production of the desired amount of thepolyolefin.

Metallocene catalysts are well known in the industry and are typicallycomprised of a transition metal component and a co-catalyst. Thetransition metal component has at least one moiety selected fromsubstituted or unsubstituted cyclopentadienyl, substituted orunsubstituted pentadienyl, substituted or unsubstituted pyrrole,substituted or unsubstituted phosphole, substituted or unsubstitutedarsole, substituted or unsubstituted boratabenzene, and substituted orunsubstituted carborane. The transition metal is selected from Groups 3,4, 5, 6, 7, 8, 9 and 10 of the Periodic Table of the Elements. Exemplaryof such transition metals are titanium, zirconium, hafnium, vanadium,chromium, manganese, iron, cobalt, nickel, and the like, and mixturesthereof. In a preferred embodiment the transition metal is selected fromGroups 4, 5 or 6 such as, for example, titanium, zirconium, hafnium,vanadium and chromium, and in a still further preferred embodiment, thetransition metal is titanium or zirconium or mixtures thereof.

The co-catalyst component of the metallocene catalyst can be anycompound, or mixtures thereof, that can activate the transition metalcomponent of the metallocene catalyst in olefin polymerization.Typically the co-catalyst is an alkylaluminoxane such as, for example,methylaluminoxane (MAO) and aryl substituted boron compounds such as,for example, tris(perfluorophenyl)borane and the salts oftetrakis(perfluorophenyl)borate.

There are many references describing metallocene catalysts in greatdetail. For example, metallocene catalysts are described in U.S. Pat.Nos. 4,564,647; 4,752,597; 5,106,804; 5,132,380; 5,227,440; 5,296,565;5,324,800; 5,331,071; 5,332,706; 5,350,723; 5,399,635; 5,466,766;5,468,702; 5,474,962; 5,578,537 and 5,863,853.

In carrying out the polymerization process of the present invention, theco-catalyst(s), if utilized, is added to the polymerization medium inany amount sufficient to effect production of the desired polyolefin. Itis preferred to utilize the co-catalyst(s) in a molar ratio ofco-catalyst(s) to metal component(s) of the olefin polymerizationcatalyst ranging from about 0.5:1 to about 10000:1. In a more preferredembodiment, the molar ratio of co-catalyst(s) to metal component(s)ranges from about 0.5:1 to about 1000:1.

The polymerization process of the present invention may be carried outusing any suitable process, for example, solution, slurry and gas phase.A particularly desirable method for producing polyolefin polymersaccording to the present invention is a gas phase polymerization processpreferably utilizing a fluidized bed reactor. This type reactor andmeans for operating the reactor are well known and completely describedin U.S. Pat. Nos. 3,709,853; 4,003,712; 4,011,382; 4,012,573; 4,302,566;4,543,399; 4,882,400; 5,352,749; 5,541,270; Canadian Patent No. 991,798and Belgian Patent No. 839,380. These patents disclose gas phasepolymerization processes wherein the polymerization medium is eithermechanically agitated or fluidized by the continuous flow of the gaseousmonomer and diluent. The entire contents of these patents areincorporated herein by reference.

In general, the polymerization process of the present invention may beeffected as a continuous gas phase process such as a fluid bed process.A fluid bed reactor for use in the process of the present inventiontypically comprises a reaction zone and a so-called velocity reductionzone. The reaction zone comprises a bed of growing polymer particles,formed polymer particles and a minor amount of catalyst particlesfluidized by the continuous flow of the gaseous monomer and diluent toremove heat of polymerization through the reaction zone. Optionally,some of the recirculated gases may be cooled and compressed to formliquids that increase the heat removal capacity of the circulating gasstream when readmitted to the reaction zone. A suitable rate of gas flowmay be readily determined by simple experiment. Make up of gaseousmonomer to the circulating gas stream is at a rate equal to the rate atwhich particulate polymer product and monomer associated therewith iswithdrawn from the reactor and the composition of the gas passingthrough the reactor is adjusted to maintain an essentially steady stategaseous composition within the reaction zone. The gas leaving thereaction zone is passed to the velocity reduction zone where entrainedparticles are removed. Finer entrained particles and dust may be removedin a cyclone and/or fine filter. The gas is passed through a heatexchanger wherein the heat of polymerization is removed, compressed in acompressor and then returned to the reaction zone.

In more detail, the reactor temperature of the fluid bed process hereinranges from about 30° C. to about 150° C. In general, the reactortemperature is operated at the highest temperature that is feasibletaking into account the sintering temperature of the polymer productwithin the reactor.

The process of the present invention is suitable for the production ofhomopolymers of olefins, particularly ethylene, and/or copolymers,terpolymers, and the like, of olefins, particularly ethylene, and atleast one or more other olefin(s). Preferably the olefins arealpha-olefins. The olefins, for example, may contain from 2 to 16 carbonatoms. Particularly preferred for preparation herein by the process ofthe present invention are polyethylenes. Such polyethylenes arepreferably homopolymers of ethylene and interpolymers of ethylene and atleast one alpha-olefin wherein the ethylene content is at least about50% by weight of the total monomers involved. Exemplary olefins that maybe utilized herein are ethylene, propylene, 1-butene, 1-pentene,1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene, 1-dodecene,1-hexadecene and the like. Also utilizable herein are polyenes such as1,3-hexadiene, 1,4-hexadiene, cyclopentadiene, dicyclopentadiene,4-vinylcyclohex-1-ene, 1,5-cyclooctadiene, 5-vinylidene-2-norbornene and5-vinyl-2-norbornene, and olefins formed in situ in the polymerizationmedium. When olefins are formed in situ in the polymerization medium,the formation of polyolefins containing long chain branching may occur.

In carrying out the polymerization process of the present invention thedinitrogen monoxide used to reduce electrostatic charge in thepolymerization medium is added in any manner. For example, thedinitrogen monoxide may be added to the preformed catalyst, to theprepolymer during the prepolymerization step, to the preformedprepolymer and/or to the polymerization medium. The dinitrogen monoxidemay optionally be premixed with the co-catalyst when utilized. Thedinitrogen monoxide is added in any amount sufficient to reduce theelectrostatic charge in the polymerization medium to a level lower thanwould occur in the same polymerization process in the absence of thedinitrogen monoxide. It is preferred to incorporate the dinitrogenmonoxide in the polymerization medium in an amount ranging from about 1ppm to about 10,000 ppm by volume.

In carrying out the polymerization process of the present invention, the=halogenated hydrocarbon may be added to the polymerization medium inany amount sufficient to effect production of the desired polyolefin. Itis preferred to incorporate the halogenated hydrocarbon in a molar ratioof halogenated hydrocarbon to metal component of the olefinpolymerization catalyst ranging from about 0.001:1 to about 100:1. In amore preferred embodiment, the molar ratio of halogenated hydrocarbon tometal component ranges from about 0.001:1 to about 10:1.

The dinitrogen monoxide and the optional halogenated hydrocarbon may beadded to the polymerization medium in any manner. The dinitrogenmonoxide and the halogenated hydrocarbon may be added to the olefinpolymerization catalyst just prior to addition to the polymerizationmedium, or added separately from the catalyst to the polymerizationmedium in any manner known in the art. For example, the dinitrogenmonoxide may optionally be premixed with the halogenated hydrocarbonprior to addition to the polymerization medium.

If a gas phase fluidized bed process is utilized for polymerization ofthe olefin, it may be advantageous to add the dinitrogen monoxide priorto the heat removal means, e.g., the heat exchanger, to slow the rate offouling of said heat removal means in addition to reducing theelectrostatic charge in the polymerization reactor.

The molecular weight of the polyolefin produced by the present inventioncan be controlled in any known manner, for example, by using hydrogen.The molecular weight control of polyethylene, for example, may beevidenced by an increase in the melt index (I₂) of the polymer when themolar ratio of hydrogen to ethylene in the polymerization medium isincreased.

Molecular weight distribution (MWD), or polydispersity, is a well knowncharacteristic of polymers. MWD is generally described as the ratio ofthe weight average molecular weight (Mw) to the number average molecularweight (Mn). The ratio Mw/Mn can be measured directly by gel permeationchromatography techniques. The MWD of a polymer is determined with aWaters Gel Permeation Chromatograph Series 150C equipped withUltrastyrogel columns and a refractive index detector. In thisdevelopment, the operating temperature of the instrument was set at 140°C., the eluting solvent was o-dichlorobenzene, and the calibrationstandards included 10 polystyrenes of precisely known molecular weight,ranging from a molecular weight of 1000 to a molecular weight of 1.3million, and a polyethylene standard, NBS 1475.

Any conventional additive may be added to the polyolefins obtained bythe present invention. Examples of the additives include nucleatingagents, heat stabilizers, antioxidants of phenol type, sulfur type andphosphorus type, lubricants, antistatic agents, dispersants, copper harminhibitors, neutralizing agents, foaming agents, plasticizers,anti-foaming agents, flame retardants, crosslinking agents, flowabilityimprovers such as peroxides, ultraviolet light absorbers, lightstabilizers, weathering stabilizers, weld strength improvers, slipagents, anti-blocking agents, antifogging agents, dyes, pigments,natural oils, synthetic oils, waxes, fillers and rubber ingredients.

The polyolefins, particularly polyethylenes, of the present inventionmay be fabricated into films by any technique known in the art. Forexample, films may be produced by the well known cast film, blown filmand extrusion coating techniques.

Further, the polyolefins, particularly polyethylenes, may be fabricatedinto other articles of manufacture, such as molded articles, by any ofthe well known techniques.

The invention will be more readily understood by reference to thefollowing examples. There are, of course, many other forms of thisinvention which will become obvious to one skilled in the art, once theinvention has been fully disclosed, and it will accordingly berecognized that these examples are given for the purpose of illustrationonly, and are not to be construed as limiting the scope of thisinvention in any way.

EXAMPLES

In the following examples the test procedures listed below were used inevaluating the analytical properties of the polyolefins herein.

a) Density is determined according to ASTM D-4883 from a plaque madeaccording to ASTM D1928;

b) Melt Index (MI), I₂, is determined in accord with ASTM D-1238,condition E, measured at 190° C., and reported as decigrams per minute;

c) High Load Melt Index (HLMI), I₂₁, is measured in accord with ASTMD-1238, Condition F, measured at 10.0 times the weight used in the meltindex test (MI) above;

d) Melt Flow Ratio (MFR)=I₂₁/I₂ or High Load Melt Index/Melt Index;

e) Residual Titanium Content in the Product. The residual titaniumcontent in the product is measured by X-Ray Fluorescence Spectroscopy(XRF) using a Philips Sequential X-Ray Spectrometer Model PW 1480. Thesamples of the polymer to be evaluated were compression molded into acircular shaped plaque approximately 43 mm in diameter so as to fit thesample holder on the spectrometer and 3 to 5 mm in thickness and havinga smooth flat surface. The molded test specimens were then placed in theXRF unit and the x-ray fluorescence arising from the titanium in thetest specimen was measured. The residual titanium content was thendetermined based on a calibration curve obtained by measurements frompolyethylene calibration specimens containing a known amount oftitanium. The residual titanium content is reported as parts per million(ppm) relative to the polymer matrix.

The Ziegler-Natta catalyst used in Example 1 was prepared in accordancewith Example 1-a of European Patent Application EP 0 703 246 A1. Thecatalyst was used in prepolymer form and was prepared in accordance withExample 1-b of European Patent Application EP 0 703 246 A1. A prepolymercontaining about 34 grams of polyethylene per millimole of titanium wasthus obtained.

Polymerization Process

The polymerization process utilized in Example 1 herein was carried outin a fluidized-bed reactor for gas-phase polymerization, consisting of avertical cylinder of diameter 0.74 meters and height 7 meters andsurmounted by a velocity reduction chamber. The reactor is provided inits lower part with a fluidization grid and with an external line forrecycling gas, which connects the top of the velocity reduction chamberto the lower part of the reactor, at a point below the fluidizationgrid. The recycling line is equipped with a compressor for circulatinggas and a heat transfer means such as a heat exchanger. In particularthe lines for supplying ethylene, 1-hexene, hydrogen and nitrogen, whichrepresent the main constituents of the gaseous reaction mixture passingthrough the fluidized bed, feed into the recycling line. Above thefluidization grid, the reactor contains a fluidized bed consisting of apolyethylene powder made up of particles with a weight-average diameterof about 0.5 mm to about 1.4 mm. The gaseous reaction mixture, whichcontains ethylene, olefin comonomer, hydrogen, nitrogen and minoramounts of other components, passes through the fluidized bed under apressure ranging from about 280 psig to about 300 psig with an ascendingfluidization speed, referred to herein as fluidization velocity, rangingfrom about 1.6 feet per second to about 2.1 feet per second.

In Example 1 the Ziegler-Natta catalyst, as described above inprepolymer form, was introduced intermittently into the reactor. Thesaid catalyst contained magnesium, chlorine and titanium. The prepolymerform contained about 34 grams of polyethylene per millimole of titaniumand an amount of tri-n-octylaluminum (TnOA) such that the molar ratio,Al/Ti, was about 1.1:1. The rate of introduction of the prepolymer intothe reactor was adjusted to achieve the desired production rate. Duringthe polymerization the additional co-catalyst, when utilized, wasintroduced continuously into the line for recycling the gaseous reactionmixture, at a point situated downstream of the heat transfer means. Thefeed rate of additional co-catalyst is expressed as a molar ratio oftrialkylaluminum to titanium (Al/Ti), and is defined as the ratio of theco-catalyst feed rate (in moles of trialkylaluminum per hour) to theprepolymer feed rate (in moles of titanium per hour). A solution ofchloroform (CHCl₃) in n-hexane, at a concentration of about 0.5 weightpercent, was introduced continuously into the line for recycling thegaseous reaction mixture. The feed rate of the optional halogenatedhydrocarbon is expressed as a molar ratio of CHCl₃ to titanium(CHCl₃/Ti), and is defined as the ratio of the CHCl₃ feed rate (in molesof CHCl₃ per hour) to the catalyst or prepolymer feed rate (in moles oftitanium per hour).

Dinitrogen monoxide (N₂O), when utilized in the following examples, wasutilized to reduce the electrostatic charge in the polymerizationmedium. The gaseous dinitrogen monoxide was introduced continuously intothe line for recycling the gaseous reaction mixture. The concentrationof dinitrogen monoxide in the polymerization medium is expressed inunits of ppm by volume.

The electrostatic charge of the fluidized bed was measured by aCorreflow Model 3400 Electrostatic Monitor (ESM) supplied by AuburnInternational, Inc. of Danvers, Mass. The electrostatic probe wasinstalled in the vertical cylindrical section of the reactor at a heightsuch as to be within the fluidized bed of polymer particles. Theelectrostatic probe measures the current flow between the polymerizationmedium and the ground. A reduction in electrostatic charge is defined asa reduction in the absolute magnitude of the measured current and/or areduction in the variability of the measured current.

Example 1

The initial process conditions are given in Table 1. The polymerizationreactor was lined out producing a interpolymer of ethylene and 1-hexenehaving a melt index of 0.6 dg/min and a density of 0.920 g/cc. The levelof electrostatic charge was measured. Thereafter, dinitrogen monoxidewas added to the reactor loop at a level of 60 ppm by volume.Trimethylaluminum was added to maintain the production rate at 160pounds per hour. The level of electrostatic charge in the polymerizationreactor was measured and it was found that the level of electrostaticcharge was reduced as a result of adding the dinitrogen monoxide.

TABLE 1 Initial Reactor Conditions for Example 1 Reactor Pressure (psig)296 Reactor Temperature (° C.) 86 Fluidization Velocity (ft/sec) 2.1Fluidized Bulk Density(lb/ft³) 16.1 Reactor Bed Height (ft) 10.9Ethylene (mole %) 26 H₂/C₂ (molar ratio) 0.145 C₆/C₂ (molar ratio) 0.146CHCl₃/Ti 0.04 Prepolymer Rate (lb/h) 0.8 Production Rate (lb/h) 160Residual Titanium (ppm) 8.5 Density (g/cc) 0.920 Melt Index, I₂ (dg/min)0.6 Melt Flow Ratio (I₂₁/I₂) 29

Example 2

The process of Example 1 is followed with the following exceptions. TheZiegler-Natta catalyst used in Example 2 is obtained from Toho TitaniumCompany, Limited under the product name THC-C. The catalyst is atitanium-based catalyst supported on magnesium chloride. This catalystis added directly to the polymerization medium. Trimethylaluminum isadded as co-catalyst to the polymerization medium. The catalyst additionrate and the co-catalyst addition rate is adjusted to produce about 200pounds of polymeric product per hour having a residual titanium contentof about 1 ppm.

Furthermore the C₆/C₂ and the H₂/C₂ molar ratios are adjusted to producean ethylene/1-hexene interpolymer having a target melt index of about0.6 dg/min and a target density of about 0.920 g/cc.

The level of electrostatic charge in the polymerization reactor ismeasured. Thereafter, dinitrogen monoxide is added to the polymerizationmedium and the level of electrostatic charge is expected to be reduced.

Example 3

The process of Example 1 is followed with the following exceptions. TheZiegler-Natta catalyst used in Example 3 is obtained from Grace Davison,Baltimore, Md. under the product name XPO-5021. The catalyst is atitanium-based catalyst supported on silica. This catalyst is addeddirectly to the polymerization medium. Triethylaluminum is added asco-catalyst to the polymerization medium. The catalyst addition rate andthe co-catalyst addition rate are adjusted to produce about 200 poundsof polymeric product per hour having a residual titanium content ofabout 1 ppm.

Furthermore the C₆/C₂ and the H₂/C₂ molar ratios are adjusted to producean ethylene/1-hexene interpolymer having a melt index of about 0.6dg/min and a density of about 0.920 g/cc.

The level of electrostatic charge in the polymerization reactor ismeasured. Thereafter, dinitrogen monoxide is added to the polymerizationmedium and the level of electrostatic charge is expected to be reduced.

Examples 4-6

The process of Example 1 is followed with the exception that in place ofthe Ziegler-Natta catalyst, there is used a metallocene catalystsupported on silica, as follows:

Example 4 bis(1-butyl-3-methylcyclopentadienyl)zirconium dichloride andmethylaluminoxane,

Example 5 bis(1-butyl-3-methylcyclopentadienyl)dimethyl zirconocene andtris(perfluorophenyl)borane,

Example 6(tert-butylamido)dimethyl(tetramethyl-η⁵-cyclopentadienyl)silanetitaniumdimethyland triphenylmethylium tetrakis(perfluorophenyl)borate.

The C₆/C₂ and the H₂/C₂ molar ratios are adjusted to produce anethylene/1-hexene interpolymer having a target melt index of about 0.6dg/min and a target density of about 0.920 g/cc.

The level of electrostatic charge in the polymerization medium ismeasured. In each of the above Examples 4-6 the level of electrostaticcharge in the polymerization medium is expected to be reduced as aresult of adding dinitrogen monoxide.

Films can be prepared from the polyolefins of the present invention.

Articles such as molded items can also be prepared from the polyolefinsof the present invention.

It should be clearly understood that the forms of the invention hereindescribed are illustrative only and are not intended to limit the scopeof the invention. The present invention includes all modificationsfalling within the scope of the following claims.

We claim:
 1. A process for polymerizing an olefin and/or an olefin andat least one or more other olefin(s) comprising contacting, underpolymerization conditions, in a polymerization medium whereinelectrostatic charge is present, the olefin and/or the olefin and atleast one or more other olefin(s) with an olefin polymerization catalystand dinitrogen monoxide, wherein the dinitrogen monoxide is present inan amount sufficient to reduce electrostatic charge in thepolymerization medium to a level lower than would be obtained in theabsence of dinitrogen monoxide.
 2. The process according to claim 1wherein the olefin polymerization catalyst comprises at least one metalselected from Groups 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and/or 13 of thePeriodic Table of the Elements, as defined herein.
 3. The processaccording to claim 2 wherein the metal is selected from the groupconsisting of titanium, zirconium, vanadium, iron, chromium, nickel andaluminum.
 4. The process according to claim 3 wherein the metal isselected from the group consisting of titanium, zirconium and vanadium.5. The process according to claim 1 wherein the olefin polymerizationcatalyst is supported on a carrier.
 6. The process according to claim 5wherein the carrier is selected from the group consisting of silica,alumina, magnesium chloride and mixtures thereof.
 7. The processaccording to claim 2 wherein the olefin polymerization catalyst isselected from the group consisting of chromium oxide catalysts,organochromium catalysts, Ziegler-Natta catalysts, olefin polymerizationcatalysts that polymerize olefins to produce homopolymers andinterpolymers of olefins having a molecular weight distribution (MWD) offrom 1 to 2.5, metallocene catalysts, cationic aluminum alkyl amidinatecatalysts, cationic nickel alkyl diimine catalysts, neutral nickel alkylsalicylaldiminato catalysts, cationic iron alkyl pyridinebisiminecatalysts and cationic titanium alkyl diamide catalysts.
 8. The processaccording to claim 7 wherein the olefin polymerization catalyst isselected from the group consisting of chromium oxide catalysts,organochromium catalysts, Ziegler-Natta catalysts, metallocene catalystsand olefin polymerization catalysts that polymerize olefins to producehomopolymers and interpolymers of olefins having a molecular weightdistribution (MWD) of from 1 to 2.5.
 9. The process according to claim 8wherein the olefin polymerization catalyst is selected from the groupconsisting of chromium oxide catalysts, Ziegler-Natta catalysts andmetallocene catalysts.
 10. The process according to claim 1 furthercomprising adding a halogenated hydrocarbon to the polymerizationmedium.
 11. The process according to claim 10 wherein the halogenatedhydrocarbon is selected from the group consisting of dichloromethane,chloroform, carbon tetrachloride, chlorofluoromethane,chlorodifluromethane, dichlorodifluoromethane, fluorodichloromethane,chlorotrifluoromethane, fluorotrichloromethane and 1,2-dichloroethane.12. The process according to claim 11 wherein the halogenatedhydrocarbon is chloroform.
 13. The process according to claim 1 whereinthe dinitrogen monoxide is added in an amount ranging from about 1 ppmto about 10,000 ppm by volume.
 14. The process according to claim 1wherein the polymerization medium is gas phase.
 15. The processaccording to claim 1 wherein the polymerization medium is slurry phase.16. The process according to claim 1 wherein the olefin is ethylene andthe at least one or more other olefin(s) is selected from the groupconsisting of olefins having 3 to 16 carbon atoms.
 17. The processaccording to claim 16 wherein the at least one or more other olefin(s)is selected from the group consisting of 1-octene, 1-hexene,4-methylpent-1-ene, 1-pentene, 1-butene and propylene.
 18. The processaccording to claim 16 wherein the interpolymer resulting from thepolymerization of ethylene and at least one or more olefin(s) comprisesethylene in an amount of at least about 50% by weight of theinterpolymer.
 19. A process for reducing electrostatic charge in thepolymerization of an olefin and/or an olefin and at least one or moreother olefin(s) in a polymerization medium in the presence of an olefinpolymerization catalyst, comprising introducing into the polymerizationmedium dinitrogen monoxide in an amount sufficient to reduceelectrostatic charge in the polymerization medium to a level lower thanwould be obtained in the absence of dinitrogen monoxide.
 20. The processaccording to claim 19 wherein the olefin polymerization catalystcomprises at least one metal selected from Groups 3, 4, 5, 6, 7, 8, 9,10, 11, 12 and/or 13 of the Periodic Table of the Elements, as definedherein.
 21. The process according to claim 20 wherein the metal isselected from the group consisting of titanium, zirconium, vanadium,iron, chromium, nickel and aluminum.
 22. The process according to claim21 wherein the metal is selected from the group consisting of titanium,zirconium and vanadium.
 23. The process according to claim 19 whereinthe olefin polymerization catalyst is supported on a carrier.
 24. Theprocess according to claim 23 wherein the carrier is selected from thegroup consisting of silica, alumina, magnesium chloride and mixturesthereof.
 25. The process according to claim 20 wherein the olefinpolymerization catalyst is selected from the group consisting ofchromium oxide catalysts, organochromium catalysts, Ziegler-Nattacatalysts, olefin polymerization catalysts that polymerize olefins toproduce homopolymers and interpolymers of olefins having a molecularweight distribution (MWD) of from 1 to 2.5, metallocene catalysts,cationic aluminum alkyl amidinate catalysts, cationic nickel alkyldiimine catalysts, neutral nickel alkyl salicylaldiminato catalysts,cationic iron alkyl pyridinebisimine catalysts and cationic titaniumalkyl diamide catalysts.
 26. The process according to claim 25 whereinthe olefin polymerization catalyst is selected from the group consistingof chromium oxide catalysts, organochromium catalysts, Ziegler-Nattacatalysts, metallocene catalysts and olefin polymerization catalyststhat polymerize olefins to produce homopolymers and interpolymers ofolefins having a molecular weight distribution (MWD) of from 1 to 2.5.27. The process according to claim 26 wherein the olefin polymerizationcatalyst is selected from the group consisting of chromium oxidecatalysts, Ziegler-Natta catalysts and metallocene catalysts.
 28. Theprocess according to claim 19 further comprising adding a halogenatedhydrocarbon to the polymerization medium.
 29. The process according toclaim 28 wherein the halogenated hydrocarbon is selected from the groupconsisting of dichloromethane, chloroform, carbon tetrachloride,chlorofluoromethane, chlorodifluromethane, dichlorodifluoromethane,fluorodichloromethane, chlorotrifluoromethane, fluorotrichloromethaneand 1,2-dichloroethane.
 30. The process according to claim 29 whereinthe halogenated hydrocarbon is chloroform.
 31. The process according toclaim 19 wherein the dinitrogen monoxide is added in an amount rangingfrom about 1 ppm to about 10,000 ppm by volume to the polymerizationmedium.
 32. The process according to claim 19 wherein the polymerizationmedium is gas phase.
 33. The process according to claim 19 wherein thepolymerization medium is slurry phase.
 34. The process according toclaim 19 wherein the olefin is ethylene and the at least one or moreother olefin(s) is selected from the group consisting of olefins having3 to 16 carbon atoms.
 35. The process according to claim 34 wherein theat least one or more other olefin(s) is selected from the groupconsisting of 1-octene, 1-hexene, 4-methylpent-1-ene, 1-pentene,1-butene and propylene.
 36. The process according to claim 34 whereinthe interpolymer resulting from the polymerization of ethylene and atleast one or more olefin(s) comprises ethylene in an amount of at leastabout 50% by weight of the interpolymer.